Several herbs have proposed antiviral activity and may aid in prevention of viral infections. More than 400 different viruses are known to cause infections including the common cold, hepatitis, mononucleosis, avian bird flu, and AIDS. Once infected with a virus, little can be done within the limits of contemporary western medicine to treat presenting symptoms. Certain medications may shorten the duration of an illness caused by a virus, or may decrease the severity of symptoms, but they are generally expensive and not readily available. Many people choose to have an annual influenza vaccination, or flu shot, but this is only 80% effective due to mutating strains of the influenza virus. Antibiotics such as penicillin and azithromycin are not effective in killing viruses, and should only be used to treat infections caused by susceptible bacteria.

Attempts have been made to isolate herbal agents that are thought to possess antiviral activity. Herbal preparations that strengthen the immune system may help the body fight off invading viruses that could otherwise cause infection, and are of particular interest to the scientific community.

Current research shows promise for arabinoxylan, a compound derived from Hyphomycetes mycelia mushroom, as an antiviral agent. Echinacea purpura has also gained mainstream acceptance for use in preventing and reducing the severity of the common cold, but scientific research has yet to provide conclusive evidence regarding efficacy.

Viruses are not considered living things, as they are only able to function while using resources of their host.

The life cycle of a virus can be simplified and divided into five stages, all of which are potential sites of action for antiviral herbals:

Attachment: The virus attaches to specific sites on the surface of human cells.

Penetration: Following attachment of the virus to membrane surface proteins, it enters the cell.

Uncoating: The virus releases its outer shell and expels its contents to prepare for replication.

Replication: Viral proteins and genetic material are assembled to make multiple copies while still inside the host cell.

Release: After many copies of the virus have been made, they are released from the host cell, often killing the host cell in the process. These newly formed viruses are now able to infect additional cells.

Potential effective antiviral herbal preparations may stimulate the immune system and assist the body in fighting off infection before the virus has had a chance to invade living cells. These preparations may also aid in disrupting the life cycle of the virus and inhibit further replication and infection of healthy cells.

Herbs that are thought to promote detoxification and elimination are often used in conjunction with antiviral herbs to further enhance action of the immune system. Some herbal preparations contain insulin, which regulates blood glucose and helps promote immunity.

Evidence of antiviral activity of selected herbals:

Andrographis paniculata: The leaves of Andrographis paniculata, an annual herb, have been used widely as part of Indian folk medicine and Ayurveda for centuries. The Chinese and Thai herbal medicine systems have also incorporated this herb, valued mostly for its "bitter" properties as a treatment for digestive problems and a variety of febrile illnesses. More recently, this herb, in its standardized extract form, has become popular in Scandinavia as a remedy for upper respiratory infection (URI) and influenza. For example, a 300 milligram Kan Jang tablet containing 4% andrographolides has been recommended to be taken four times daily for cold treatment (for a total daily dose of 48 milligrams andrographolides). Lower doses have been evaluated for respiratory infection prevention; for example, a single 200-300 milligram standardized tablet taken daily. Use appears to be safe for up to two weeks. Higher doses may be unsafe, leading to significant side effects. Kulichenko et al. carried out two randomized parallel-group trials of the SHA-10 extract of andrographis (Kan Jang, Swedish Herbal Institute) in adults diagnosed with influenza. Both studies found significant improvements in reduction of duration of influenza symptoms (1-2.5 days sooner, depending on particular symptom, p< 0.01). Although the study suffers from a poorly described randomization procedure and a lack of a standardized outcome measure for symptoms, it does seem to provide preliminary evidence that andrographis extract may be effective not only for standard URI treatment but also specifically for influenza treatment.

Apple juice: Freshly prepared apple juice has appreciable antiviral activity, but the activity may decline more readily than that of commercial juice in response to heat and storage.

Astragalus: Astragalus is an extremely versatile herb which may act as an immune strengthener. It is a commonly used herb in traditional Chinese medicine and is used as a component of many immune-supporting formulas, whether prepared as a sliced and boiled herb in food preparations, in extracts, or in capsules. The IL-2 inducing activity of the triterpene saponins found in astragalus might be the mechanism involved in the immunomodulatory and anticancer effects of astragalus species.

Echinacea: Echinacea may boost the immune defenses in various ways. It contains three compounds with specific antiviral activity: caffeic acid, chicoric acid, and echinacin. It strengthens the body's local defenses by use of a substance, echinacein, that deactivates germs' tissue-dissolving enzyme. This prevents germs from spreading and infecting other body tissues. In one study, echinacea stimulated production of white blood cells and phagocytes, and increased macrophage germ-killing activity. A University of Munich study demonstrated that echinacea boosted production of infection-fighting T-lymphocytes up to 30% more than standard immune-supportive drugs. In Germany echinacea is used to treat flu, colds, bronchitis, tonsillitis, ear infections and whooping cough. Root extracts of echinacea are believed to boost interferon levels, vital to the body's defenses.

Elderberry (Sambucas nigra L.): Elderberry has been used has been used as a remedy for flu, cough, colds, and upper respiratory infections for over 2500 years. Recent studies demonstrate black elderberry's effectiveness against all strains of influenza virus. A constituent present in black elderberry (with actions similar to neuraminidase inhibitors oseltamivir and zanamivir) prevents the spread of virions from infected cells to new cells. Black elderberry is most effective in either a syrup form or in lozenges.

Forsythia (Forsythia suspensa): Forsythia is a traditional Chinese herb used for treating colds, flu, and other viruses. It is often mixed with honeysuckle and sometimes lemon balm and/or ginger as a tea.

Garlic (Allium sativum): Garlic may possess antiviral activity. Experts claim it is most effective in its natural form, and they recommend juicing and drinking several cloves as needed. Garlic capsules are available and are preferred by those who find the taste of fresh garlic unpleasant. Experts recommend taking 2 capsules daily for prevention of infection. Garlic contains several antimicrobial compounds including allicin, reportedly one of nature's strongest broad-spectrum antibiotics. Studies have shown that garlic inhibits the growth of many types of bacteria, including Bacillus, Brucella, Citrobacter, E. Coli, Hafnia, Klebsiella, Salmonella typhi, Shigella, Vibrio cholerae, and various forms of Staphylococcus and Streptococcus. Further studies are needed before any firm recommendations can be made.

Grape seed extract (GSE): GSE
is a general antimicrobial agent with specific antiviral properties. It is best known for its application against Candida albicans, an organism responsible for fungal infections. Although not proven by scientific research, it may be effective against a long list of other microorganisms as well, including herpes simplex type 1 virus, and influenza A virus. GSE may be used in liquid concentrate form or in capsules. GSE may be taken internally, in minute doses such as 2 to 4 drops twice daily diluted in at least 4 ounces of carrot, orange, pineapple or grapefruit juice.

Green tea: Certain constituents called catechins found in green tea have been studied for their ability to inhibit influenza virus replication and their direct virucidal effects. One study evaluated polyphenolic compound catechins ((-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG) and (-)-epigallocatechin (EGC)) from green tea for their ability to inhibit influenza virus replication in cell culture and for potential direct virucidal effect. Among the test compounds, the EGCG and ECG were found to be potent inhibitors of influenza virus replication. It has been suggested that the antiviral effect of catechins on influenza virus is mediated not only by specific interaction with HA, but via alteration of the physical properties of the viral membrane.

Honeysuckle (Lonicera japonica) is often used in China to treat bacterial and viral conditions. It is taken as a liquid from flower extracts or as a tea.

Isatidis (Isatis tinctora): This herb is one of the best-known traditional Chinese medicine antiviral herbs. Isatidis may be a remedy for any virus but appears to be especially good for hepatitis, because it helps reduce both swelling and liver inflammation. Isatidis is mild and can be used in children or those who do not tolerate heat well. Isatidis may also be a good anti-bacterial agent.

Leptotaenia (Leptotaenia dissecta Nutt.): Available in both capsules or as a liquid extract, leptotaenia is an herb known to be useful in treating pneumonia, flu, colds, and bronchitis, as well as viruses such as Herpes simplex I and II and hepatitis C.

Licorice root (Glycyrrhiza glabra): Licorice root has been used to prevent and remedy infections, fevers and inflammation. It has broad antimicrobial activity against viruses, bacteria, yeast and fungi. Licorice contains at least eight antiviral and 25 antifungal substances. Licorice also possesses antiviral compounds that promote interferon release. By itself, licorice is a dynamic herb that should only be used for short periods of time.

Olive leaf (Olea europea): This herb has general antimicrobial and antiviral properties. It usually comes in powder form in capsules.

Schizandra (Schizandra chinensis):
This herb has been used in traditional Chinese medicine as an antiviral herb, specifically in cases of viral hepatitis. Schizandra may be taken in capsule form or the dried berries may be found in herb shops.

St.John's wort: Hypericin, a constituent of St. John's wort, has been extensively studied as an antiviral. While hypericin has been shown to be effective in inactivating enveloped viruses, such as hepatitis B and C, and cytomegalovirus, it has not been effective against non-enveloped viruses, such as hepatitis A, or parvovirus B-19.

Vitamin E: Vitamin E is a commonly encountered nutritional supplement with antioxidant properties. Based on animal study, vitamin E may reduce PGE2 production, which in turn leads to enhancement of Th1 cytokines.

The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.